In some cases, a color of metallic painting, pearl color painting and the like to be used in painting for a car and the like is seen to be different depending on a direction of an observer under the influence of a brilliant material in an inner part. For this reason, a multi-angle colorimeter for carrying out illumination or light reception at a plurality of angles is used for evaluation of the painting (evaluation of a paint color).
In other words, the metallic painting and the pearl color painting which is to be used in painting for a car and the like is constituted by containing, in a painted film, a flaky aluminum piece and mica piece which is referred to as a brilliant material and produces a so-called metallic effect and pearl effect. This is caused by the fact that contribution of the brilliant material to a reflection characteristic is varied depending on illuminating and observing directions. A multi-angle colorimeter having a multi-angle geometry (an optical configuration) is used for evaluating the metallic painting and pearl color painting (colorimetry). The multi-angle colorimeter serves to carry out illumination over a measurement plane of an object to be measured in a plurality of directions to perform light reception in one direction (multi-direction illumination and one direction light reception) or to carry out the illumination over the measurement plane of the object to be measured in one direction to perform the light reception in a plurality of directions (one direction illumination and multi-direction light reception).
If a measuring target is a sample having a curvature, for example, a bumper of a car or the like, however, there is a high possibility that a posture error in which a sample normal and a reference axis of a colorimeter are not coincident with each other in measurement might be made. Above all, an angular direction which is close to a regular reflected light has a great angular dependency of a reflection characteristic. For this reason, the influence of the error cannot be ignored.
In order to reduce the posture error, therefore, there is proposed the technique in which an optical base unit including a measuring optical system is held by an elastic body such as a spring with respect to a housing and an illumination and light reception geometry is maintained to be constant without depending on a contact angle of a sample and the housing to reduce the measurement error by the method disclosed in Japanese Patent Application Laid-Open No. 2002-5830,for example.
As another well-known technique, moreover, there is also the technique for suppressing the posture error of the colorimeter by employing the structure in which a plurality of contact pins are disposed on a sample contact surface and measurement trigger is applied if all of them are pressed uniformly.